Method and device for convolutive encoding and transmission by packets of a digital data series flow, and corresponding decoding method and device

ABSTRACT

A method for convolutive encoding process and transmission by packets of a digital data series in which a set of successive n=K−1 bits are discriminated to form a current word of n bits. A stable starting binary value for the convolution encoding is defined and the current word is subjected to a convolutive encoding of depth K, at each bit value i(k) corresponding thus an encoded symbol S(k)={a(k);b(k)}. A packet of encoded symbols is formed by concatenating the encoded symbols and the stable constraint value is assigned to the convolutive encoding at the packet end. An encapsulation message the packet of encoded symbols is generated and the encapsulation message and packet of encoded symbols are transmitted in the same message for decoding and use. Decoding of the encoded symbols takes place in relation to the encapsulation message value and packet of encoded symbols length.

This application is a divisional of U.S. application Ser. No.09/362,109, filed on Jul. 28, 1999, now U.S. Pat. No. 6,683,914.

FIELD OF THE INVENTION

The invention concerns a method for convolutive encoding andtransmission by packets of a digital data series, the method and thecorresponding decoding device.

BACKGROUND OF THE INVENTION

The technical area relating to the transmission of digital data,particularly by a radio or satellite channel has seen its importancetake a growing significance, in the last decade.

A basic constraint is the conservation of the integrity of this data andfinally of the intelligibility of the information carried during thetransmission of this data. Indeed, in the case where physicaldisturbances, (in particular of a radio-electric nature), occur, thetransmitted message is corrupted and may become unusable.

In order to protect against such risks, numerous applications using adigital data transmission method, audio and/or video transmission byterrestrial or satellite broadcasting, it is prudent to call forencoding processes of transmitted data, and in particular of convolutiveencoding.

The convolutive encoding process represents a high performance errorcorrecting encoding process class, which can be applied to operations ofdata series transmission, in a transmission channel disrupted by aGaussian type of noise, such as the transmission channel by radioconnection between a terrestrial station and a satellite station.

Generally speaking, to encode a message with a convolutional type ofencoding, not only the current data present at the instant t at input tothe encoder, current bit of rank k, is used, but also the n data valuesor bits of the previous rank. A memory effect of order n to encode thisdata is thus introduced. In referring to such a principle, it appearsthat every transmitted message takes account of the previous content ofthe message. The previous content of the message at the instant t ismemorised in a memory updated with each current bit. The size of thismemory is defined by the length of the previous content, which is calledconstraint length of the code used and designated by K, with K=n+1.

Referring to FIG. 1, relative to a known convolutive encoding device ofthe prior art, a memory formed for example by a shift register providedwith elementary cells enabling n successive bits to be memorised, thebit previous to the current bit i(D−1) up to the bit i(D−n) of rank D−n,then enables a logic processing, by an exclusive OR type of logicoperator for example, of the current bit i(D) by several previous bitsof a specified rank. In the usual way and in order to reinforceprotection against errors, it is appropriate to generate two or moreencoded values a(D) and b(D), correlated by two distinct constraints.Each encoded value associated with a(D);b(D) thus constitutes arepresentative symbol S(D)={a(D);b(D)} of the current data i(D). In theexample of FIG. 1 given as a non-restrictive example, the depth ofencoding is K=7. The successive encoded values a(D) and b(D) are givenby the relations:a(D)=i(D)g ₁(D) with g₁=171 octb(D)=i(D)g ₂(D) with g₂=133 oct

The notation oct designating the octal notation.

Thus the aforementioned convolutive encoding and the corresponding errorcorrecting codes can be used by means of simple structure circuits.

The decoding process of such codes, and consequently the transmissionerror correction, necessitate on the other hand the use of much morecomplex functions.

In particular, in the case of convolutive encoding, the optimum decodingof a code obtained in this way can be obtained by means of the use of adecoding process according to the VITERBI algorithm. The principle ofthe aforementioned algorithm is based on the fact that the encodercorresponds in fact to a state machine or robot of simple structure orhaving at least a limited number of states.

According to the aforementioned principle, the receiver-decoder searchesfor an estimation at each instant of the state of the encoder, todetermine the transmitted sequence during the reception of all new data,i.e. of the current bit of successive rank.

A universal decoding process of such a code then consists of comparingthe received sequence, at the current instant, with all the possiblesequences which can be transmitted and to choose, from amongst these,that which presents a maximum probability.

In order to do this, the most probable a posterior coded sequence isthen determined by determining the smallest distance value between thereceived sequence and the possible coded sequences, the notion ofdistance value being defined according to the notion of Hammingdistance.

A lattice diagram enables the developments of the state of the encoderto be displayed as a function of time, for the value of the data ofinput bit of rank k, each lattice node representing a possible state ofthe encoder and of the encoded value. For each new value received, theHamming distance is then calculated at each point of the lattice. Thisdistance is accumulated with the calculated value at this same pointduring the evaluation of the previous value. To determine the mostprobable sequence then consists in returning to the lattice diagram andlooking for the decoded values which correspond globally to the smallestaccumulated Hamming distance.

For a more complete description of the VITERBI algorithm, reference ismade to the article entitled The Viterbi Algorithm published by G. DavidFORNEY, Jr., Proceedings of the IEEE vol.61, No. 3, March 1973, pp. 268to 278.

The search process of the decoded values which correspond globally tothe smallest Hamming distance, by bringing into the diagram a data andsequence value with the following data and sequence value, necessarilyinvolves a decoding and by corollary a highly continuous encodingprocess. In other words, if it is desired to process a decoding of asequence generated by means of a convolutive encoding, it is in no wayconceivable then to interrupt the recovery of the encoding or decoding.Such an interruption, introducing discontinuities in the latticediagram, would then have the effect, because of such a discontinuity, ofdestroying any chance of finding the path for which the Hamming distanceis minimal and consequently the most probable sequence.

OBJECTS OF THE INVENTION

The object of the present invention is to find a solution to thedisadvantages of the prior art encoding/decoding processes byimplementing a method convolutive encoding and transmission by packetsof a digital data series flow and a method for decoding of a digitaldata series flow encoded by convolutive encoding and transmitted bypackets according to this convolutive encoding method, in the absence ofany degradation of corrective power inherent in the decoding process bymeans of a VITERBI algorithm, which is reserved for the decoding ofcontinuous data flow encoded by convolutive encoding.

Another object of the present invention is to implement a method for aconvolutive encoding and transmission by packets of a digital dataseries flow coming from separate encoders, this digital data beingtherefore a priori uncorrelated, and a corresponding method for decodingenabling the corrective power inherent in the convolutive encoding anddecoding process according to a VITERBI algorithm to be conserved,although it is reserved to the decoding of continuous data flow encodedby a convolutive encoding.

Another object of the present invention is finally to implement adecoding device for a digital data series flow encoded by convolutiveencoding and transmitted by packets, according to the method fordecoding which is the object of the present invention.

SUMMARY OF THE INVENTION

The method for convolutive encoding and transmission by packets of adigital data series flow, a succession of q bits i(k) of specifiedvalue, by means of a convolutive encoding of depth K, which is theobject of the present invention, is noteworthy in that it consists atleast of discriminating in the series flow a set of n=K−1 successivebits, n<q, to form a current word of n bits, in defining for theconvolutive encoding process a stable starting binary value, subjectingthe current word of n bits to a convolutive encoding process of depth K,at each bit value i(k) corresponding to a first a(k) and a second b(k)encoded value, the set of these first and second encoded valuesconstituting an encoded symbol S(k)={a(k),b(k)} representative of theconsidered bit i(k), forming from the q encoded symbols a packet ofencoded symbols by concatenation of these encoded symbols, assigning theconvolutive encoding process the aforementioned stable value as theconstraint value at the end of the packet, generating at least oneencapsulation message of the packet of encoded symbols and transmitting,in the same message, the aforesaid encapsulation message and theaforesaid packet of encoded symbols for decoding and use, then to repeatthe previous operations for each current packet of the flow of bits.

The method, which is the object of the present invention, for decoding adigital data series flow transmitted by packets in accordance with theencoding process according to the invention thus consists of at least,during reception of the encapsulation message and of the packet ofencoded symbols, in discriminating the encapsulation message in order togenerate an envelope logic signal having a first binary value prior tothe start and after the end of the packet of encoded symbols and asecond binary value during the reception of the encoded symbols,submitting the envelope logic signal and the encoded symbols to a logicprocess enabling to generate pause symbols of specified value andsuccessive rank for the first binary value of the envelope logic signal,and successive validated encoded symbols, S′(k)={a′(k);b′(k)} ofsuccessive rank k corresponding to the encoded symbols S(k) for thesecond binary value of the envelope logic signal, to submit the pausesymbols and the validated encoded symbols of successive rank to acontinuous VITERBI type decoding, the aforesaid pause symbols enablingthe continuity of the decoding lattice to be obtained by imposing astable state between two packets of successive encoded symbols.

The decoding device for a digital data series flow encoded byconvolutive encoding and transmitted by packets, representative of thisencoded digital data, which is the object of the present invention, eachrepresentative packet of the digital encoded data comprising a currentpacket of successive encoded symbols associated with at least oneencapsulation message adapted to signalize the transmission of thiscurrent packet, is noteworthy in that it comprises at least onediscrimination module of the aforesaid encapsulation message enabling anenvelope logic signal of the current packet to be generated, having afirst and a second logic value, a logic processing module of theenvelope logic signal and of the encoded symbols representative of thisdata, the aforesaid logic processing module enabling a continuous flowof digital data constituted by the aforesaid packet of successiveencoded symbols to be generated, a VITERBI decoding module receiving thecontinuous flow of digital data, the aforesaid decoding module beingupdated to the pause state from the envelope logic signal for eachcurrent packet.

BRIEF DESCRIPTION OF THE DRAWINGS

The method for encoding process, the method and the method for decoding,which are the object of the present invention, will be better understoodby reading the description and observation of the drawings below, inwhich, other than FIG. 1 relative to the prior art:

FIG. 2 a shows a general flow chart of the method for convolutiveencoding and transmission by packets of a continuous data flow accordingto the object of the present invention;

FIG. 2 b shows, in a non-limitative embodiment, the structure of packetsof encoded symbols transmitted by the use of the method for encoding, asillustrated in FIG. 2 a;

FIG. 3 a shows a general flow chart of a method for decoding for encodedsymbols and transmitted in accordance with the method of the presentinvention, illustrated in FIG. 2 a;

FIG. 3 b shows in an illustrative way a generation stage of an envelopelogic signal enabling to implement the decoding method illustrated inFIG. 3 a;

FIG. 3 c shows a lattice diagram relative to a VITERBI decoding processapplied to digital data encoded by convolutive encoding and transmittedin packet mode, in accordance with the method which is the object of theinvention;

FIG. 4 a shows, in the form of a synoptic diagram, a decoding device inaccordance with the object of the present invention;

FIGS. 4 b to 4 e show different embodiments particular to a logicprocessing module of encoded symbols and of the envelope logic signal,as a function of the pause value assigned to the encoding and to thedecoding respectively and the logic value of the envelope logic signalin the active state;

FIG. 5 shows a diagram given as an example of a generator module of theenvelope logic signal; and

FIG. 6 shows a timing chart of signals applied at the output of aVITERBI decoding device in order to enable the discrimination bysynchronisation of data decoded from validated encoded symbols.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A more detailed description of the convolutive encoding process and oftransmission by packets of digital data series flow, in accordance withthe object of the present invention, will now be given in connectionwith FIGS. 2 a and 2 b.

In a general way, it is shown that each packet of digital data P_(j) tobe encoded and to be transmitted is made up of a succession of q bits,i(k), k designating the successive rank of each of the constituent bitsof the data packet.

In a general way, it is shown that the process, the object of thepresent invention, uses a convolutive encoding process of depth K, asmentioned previously in the description.

As shown in FIG. 2 a, the method, the object of the present invention,consists then, in a stage a), to discriminate in the data series flow,i.e. for every corresponding packet P_(j), a set of n=K−1 successivebits, n being of course less than q, to form a current word of n bits.

The encoding method, the object of the present invention, consists also,in stage b) to define, for the aforementioned encoding process, aso-called start stable binary value, enabling in fact to initialise theencoding process as will be described in a more detailed way below inthe description.

By reference to FIG. 1, it is shown that the stage a) can be performedby the use of a chain of memory cells comprising n memory cells intendedto memorise the set of n successive bits in the data series flow and byshifting each bit of rank k of the word of n bits thus constituted. Itis understood in particular that the aforementioned memory cells chaincan to advantage be achieved by a shift register, which enables from thedata series flow the sampling of a sliding window forming theaforementioned word of n bits.

With regard to stage b) consisting of defining, for the convolutiveencoding process, a stable starting binary value, it is shown that thisbinary value is to advantage assigned to the set of constituent memorycells of the aforementioned chain of memory cells. Thus, the encodingprocess in accordance with the object of the present invention, consistsin fact of previously initialising at the creation of the first word ofn bits in the aforementioned packet P_(j), the convolutive encodingprocess itself with the retained stable binary starting value. It isunderstood that in the absence of the packet P_(j), the set ofconstituent memory cells of the memory cells chain is then positioned atthe stable starting value, the value 0 or the value 1, as will bedescribed later in the description.

The stages a) and b), as shown in FIG. 2 a, are then followed by a stagec) consisting of subjecting the current word of n bits thus formed to aconvolutive encoding process of depth K, so that to each value of biti(k) correspond a first a(k) and a second b(k) encoded value, theseencoded values constituting an encoded symbol marked S(k)={a(k);b(k)},this symbol being representative of the considered bit i(k).

The symbols S(k) can be obtained in an advantageous way from an encodingprocess such as shown in FIG. 1 for example. It is shown in particularthat the encoding process is thus used successively for the set of wordsof n bits constituting the considered packet P_(j) according to theprocess indicated previously in the description.

With the stage c) is then associated a stage d) consisting of forming,from the encoded symbols, the number of encoded symbols being equal tothe number of bits constituting the considered packet P_(j), a packet ofencoded symbols, marked PS_(j), by concatenation of these encodedsymbols. The concatenation process used consists in concatenatingsuccessively the successive values a(k) and b(k), constituent of eachencoded symbol.

The aforementioned stage d) is itself followed by a stage e) consistingof assigning to the convolutive encoding process the stable value, theaforementioned so-called starting value. In these conditions, it isunderstood that the stable value re-applied to the encoding processenables in fact this value to be applied not only as the starting valuefor every later data packet P_(j+1) likely to be subjected to theencoding process and the transmission by packets at any instant, butalso as the constraint value to the encoding process in order to purgethe memorised value in each memory module from the end of the encodingprocess of the current data packet P_(j), according to the method whichis the object of the present invention.

From the obtaining of the packet of encoded symbols PS_(j) in the staged), and indeed from the assignment to the encoding of the stablestarting value in the stage e), the encoding method according to theinvention consists then in generating at least one encapsulation messageof the packet of encoded symbols. This encapsulation message, markedC_(j), can consist, of a synchronisation word SY_(j) and a length valueL_(j) of the considered packets of symbols PS_(j).

The encapsulation message C_(j) having been created, the method, theobject of the present invention, consists then of transmitting, in thesame message, the aforementioned encapsulation message C_(j) and theencoded packet of symbols PS_(j), as shown in the stage g) of FIG. 2 a.This transmission in the same message can consist of carrying out aconcatenation of the encapsulation message C_(j) and of the packet ofencoded symbols PS_(j), then to carry out the transmission of theresulting message thus obtained for decoding and use. Of course, in theabsence of later data packets P_(j+1), the convolutive encoding processand the transmission by packets of a digital data series flow accordingto the object of the present invention, leads to an end stage, shown inFIG. 2 a, whereas, in the presence of a later digital data packet ofrank j+1, the previous operations a) to g) are repeated for theaforementioned packet, becoming the current packet, constituent of theflow of bits, and eventually for every successive packet.

In FIG. 2 b, a message resulting from the concatenation of anencapsulation message C_(j) and from the encoded symbols PS_(j) has beenshown. In a standard way, it is shown that the encapsulation message canconsist of an encoded synchronisation word SY_(j) in a field of 4 octetsfor example and a length field of the packet of encoded symbols PS_(j),length field marked L_(j), which can be encoded for example over 24octets. Of course, in the resulting message such as shown in FIG. 2 b,the length of the field corresponding to the packet of encoded symbolsPS_(j) corresponds to the length value of the encoded symbols containedin the field L_(j).

The method for convolution encoding and transmission by packets of adigital data flow, in accordance with the object of the presentinvention, such as described in connection with FIGS. 2 a and 2 b, canbe used for the encoding of packets transmitted in an asynchronous wayalong a transmission line, these packets being able in particular toemanate from separate and uncorrelated transmitters.

In these conditions, it is understood that the convolutive encodingprocess used in the method for convolutive encoding and transmission bypackets, according to the object of the present invention, starts infact for every data packet P_(j) with a convolutive encoder positionedin the previously mentioned stable state. In these conditions the nmemory elements are positioned for example, either with the value 0, orwith the value 1. Similarly, in order to guarantee the whole of theprocessing of a packet, the convolutive encoding process used is thenpurged by the application to the encoding process of a specified fixedvalue. In the simplest embodiment, the specified fixed value enablingthe encoding process to be purged consists in using the so-calledstarting stable value, this value being thus assigned to the encodingprocess beforehand and later to the encoding of a packet itself. In anon-limitative advantageous embodiment, it is pointed out that when thestarting stable value is chosen equal to zero, the n memory cells beingpositioned with the value zero, in the same way and in accordance with aparticular way of implementing the method which is the object of thepresent invention, it is then necessary to add at least n aforementionedso-called starting stable values, at the end of the packet, in order topurge the n memory cells of the considered chain of memory cells. It isthe same when the chosen stable value has a value 1. In a simplifiedversion, it is shown that the method, the object of the presentinvention, as a non-restrictive example, can then simply consist ofadding by concatenation at the start and at the end of the data packetP_(j), n considered stable values. However, in such a version, the valueof encoded length in the field of length L_(j) is, preferably, the valuewhich corresponds to the actual length of the data packet P_(j), takingaccount of the concatenated stable values at the packet start and end.An encoding device enabling the creation of a resulting message such asdescribed in connection with FIG. 2 b will not be described in detailbecause such a device uses standard elements enabling simply, fromconcatenation modules of the data packets P_(j) of n stable values atthe packet start and end, to supply in fact a convolutive encoder suchas described in FIG. 1.

A method for decoding a digital data series flow encoded by convolutiveencoding and transmitted by packets, according to the method which isthe object of the present invention such as described in FIGS. 2 a and 2b, will be now given in connection with FIG. 3 a and FIG. 3 b.

In a general way, it is recalled that in a non-restrictive preferentialembodiment, the use of the encoding process, the object of the presentinvention, has the effect of generating the transmission of a resultingmessage such as shown in FIG. 2 b. This resulting message includes theencapsulation message C_(j), relating to the data packet P_(j), and themessage constituted by the encoded symbols PS_(j) relating to the sameaforementioned data packet.

In these conditions as shown in FIG. 3 a, the decoding process, theobject of the present invention, consists, in the reception of theencapsulation message C_(j) and of the aforementioned encoded symbolsPS_(j), the reception stage being marked a′ in FIG. 3 a, to carry out atleast one stage b′) consisting of discriminating the encapsulationmessage C_(j) in order to generate an envelope logic signal E_(j) havinga first binary value prior to the start and subsequently at the end ofthe packet of encoded symbols PS_(j), and a second binary value duringthe reception of the aforementioned packet of encoded symbols PS_(j).

The stage b′) is itself followed by a stage c′) consisting of subjectingthe envelope logic signal E_(j) and the encoded symbols S(k) to a logicprocessing enabling the generation, on the one hand, pause symbols ofspecified value and successive rank for the first logic value of theenvelope logic signal E_(j) and, on the other hand, of the validatedencoded symbols of successive rank k, these validated encoded symbolsmarked S′(k)={a′(k);b′(k)} for the second binary value of the envelopelogic signal. Of course, the validated encoded symbols correspond to theencoded symbols S(k) originating during the second binary value of theaforementioned envelope logic signal.

It is understood in particular that the logic processing, marked * inFIG. 3 a, enables carrying out in fact the operationS(k)*E _(j)

-   -   this logic operation being defined as a function, on the one        hand, of the effective logic value of the first logic value of        the envelope signal, and, on the other hand, as a function of        the pause value allocated to the convolutive encoding process        itself, as will be explained later in the description.

Finally, the stage c′) shown in FIG. 3 a is followed by a stage d′)consisting of subjecting the pause symbols and validated encoded symbolsof successive rank to a continuous VITERBI type decoding, the pausesymbols enabling the continuity of the decoding lattice to be ensured byholding a stable state from the stable starting value between twopackets of successive encoded symbols.

It is understood of course that the logic processing applied to theencoded signals from the envelope logic signal enables in fact, theVITERBI decoding process itself, to generate specific values of pausesymbols corresponding to the stable starting values, in order to enablea continuous VITERBI type of coding to be carried out.

The creation process of the envelope logic signal, from theencapsulation message C_(j) such as described in connection with FIG. 3a to the stage b′), will be now described in connection with FIG. 3 b.

By reference to the aforementioned figure, it is shown that on detectionof the synchronisation word SY_(j), for example by comparison of thefield relating to the synchronisation word in the encapsulation messageC_(j) to a reference word, then on reading the length value L_(j), thecreation process of the envelope logic signal E_(j) can simply consistof generating a logic signal with a first binary value, the value zerofor example shown in FIG. 3 b, from the recognition of thesynchronisation word SY_(j) for example, then to pass to thecomplemented value of this first logic value, the value 1 in FIG. 3 b,at the end of a specified number of clock cycles corresponding to theeffective transmission of the aforementioned field of length L_(j). InFIG. 3 b, the aforementioned clock signal is marked CK. The complementedvalue, the value 1 relating to the envelope logic signal correspondingto a second logic value of this latter, can then be held for theduration of the number of clock cycles corresponding to the reading ofthe successive encoded signals of the packet of symbols PS_(j), thenbrought back to the first logic value, the value zero, from the end ofthe reading process previously mentioned in coincidence with the end ofthe reading of the aforementioned packet of symbols.

The VITERBI decoding process in the stage d′) mentioned in connectionwith FIG. 3 a is then the following.

The continuity in the lattice, the diagram specific to the VITERBIdecoding, is obtained by holding and imposing the stable state from theaforementioned stable value between two consecutive packets of ranks jand j+1. This stable state is that which, definitely, represents theencoded data emitted at the start and at the end of the packet, thestate which is held between two successive packets.

In a lattice, there only exist two states corresponding to thesecriteria, the state zero and the state 1 corresponding to theaforementioned stable values as a function of the depth K of theencoding process used. This state is equal to 3 for K=3 and to 63 forK=7.

Conceptually, the VITERBI algorithm guarantees indeed that, when thelattice is in state zero and that it always receives zeros, the state ofthis latter does not change, no divergence being introduced between thereceived value and the expected value. It is the same for a state 1 withthe reception with a value 1.

Furthermore, if the encoding process uses as stable starting or pausevalue the zero value taken as constraint value, by construction, theVITERBI algorithm implies that the most probable path at the end ofreception of a packet of encoded symbols PS_(j) leaves the node or thezero state of this lattice and that the later packet will commence atthe same node. The same principle is of course applicable for aconstraint or pause value equal to 1, the packet starting and end statecorresponding then to n values 1.

A representation of a lattice in a VITERBI decoding process for K=3 witha constraint value or stable value equal to zero is shown in FIG. 3 c,for the successive packets PS_(j−1), PS_(j).

The method for convolutive encoding and transmission by packets of adigital data series flow and the corresponding decoding method, theobjects of the present invention, enable, at the level of the decodingprocess, to force the lattice to stay at the stable state or the pausestate established from the stable starting values between two successivepackets, and therefore never to interrupt the processing of the data,even in the packets transmission mode.

As the transmission packets mode consists of transmitting data in burstsand to space these bursts in time, this mode therefore induces breaks inthe logic continuity of the data transmitted and is not able therefore apriori to be subjected to a VITERBI type of decoding, the flow of datain the methods, the object of the present invention, is neverinterrupted. Indeed, the pause state appears as the natural state as theresult of the method and it is not therefore necessary to modify thecore of the design of the VITERBI decoder used in order to operate inpackets mode.

It is understood, just as by the creation of the envelope logic signalfrom the encapsulation message, the logic processing between the encodedsymbols and the envelope logic signal enables such a continuity to besimply ensured.

It is understood of course that the process or operating mode of theencoder rigorously follows the process or operating mode of the logicprocessing at the decoding level.

Different modes of carrying out the logic processing will now be givenin connection with the form of the encapsulation signal and the pausevalue retained.

According to a first embodiment of the aforementioned logic processing,for a pause state just as for a first logic value of the envelope logicsignal corresponding to the signaling of the packet start and end equalto the value zero, and for a second logic value of the envelope logicsignal equal to the value 1, the logic processing is a logic processingby an AND logic function.

In such a case, if the envelope logic signal is inactive, i.e. the firstlogic value zero, the entering data is replaced by a zero value, whichof course holds the lattice at the zero state, i.e. the pause state.

In a second embodiment, for a pause state equal to the value 1, a firstlogic value preceding the start and subsequent to the end of the packetof encoded symbols of the envelope logic signal equal to the value 1,and for a second logic value, the envelope activity, equal to the value0, the logic processing carried out between the envelope logic signaland the encoded symbols S(k) is a type OR logic function with thecomplemented envelope logic signal.

In a third embodiment, for a pause state and a first logic value of theenvelope logic signal equal to the 0 value and for a signal representingthe envelope activity , to the second logic value, equal to the value 1,the logic processing carried out between the envelope logic signal andthe encoded symbols is an AND logic function with he complementedenvelope logic signal.

In a fourth embodiment, for a pause state and a first logic value of theenvelope logic signal equal to the value 1 and for an activity signal ofthe envelope corresponding to the second logic envelope value equal tothe value zero, the logic processing between the symbols S(k) and theenvelope logic signal is an OR type function with the aforementionedenvelope logic signal.

Other embodiments can be imagined.

A more detailed description of a decoding device for a digital dataseries flow encoded by convolutive encoding and transmitted by packets,according to the encoding process previously described in thedescription, will now be given in connection with FIGS. 4 a to 4 d.

Taking account of the structure of the resulting transmitted message,such as shown in FIG. 2 b, the device such as shown in FIG. 4 a cancomprise to advantage a discrimination module 1 for the encapsulationmessage C_(j) enabling an envelope logic signal E_(j) to be generated aspreviously mentioned in relation to the current packet of symbolsPS_(j). The envelope logic signal E_(j) has a first and second logicvalue as previously mentioned.

The decoding device comprises furthermore a logic processing module 2 ofthe envelope logic signal and of the encoded symbols S(k) representativeof the encoded data. The module 2 receives the envelope logic signalE_(j) and the symbols S(k), the logic processing module 2, by the use ofthe aforementioned logic functions, enables a continuous flow of digitaldata constituted by the packet of successive encoded symbols to begenerated to which can be associated the pause symbols, marked Sr(k)corresponding to the pause state.

Finally, the decoding device includes a VITERBI decoding module 3receiving the continuous flow of aforementioned digital data, thisdecoding module being thus updated to the pause state from the envelopelogic signal, by means of the introduction of the pause symbols S(k),this operation being of course carried out for each current packet PSj.

In a general way, it is shown that the logic processing module 2includes a first logic cell 20 receiving, in a first input, each firstelement of symbols a(k) and, in a second input, the envelope logicsignal E_(j), this first logic cell 20 delivering a first element ofvalidated symbols a′(k). Moreover, the logic processing module includesa second logic cell 21 receiving, in a first input, each second elementof symbols b(k) and, in a second input, the envelope logic signal E_(j),and delivering a second element of validated symbols b′(k).

The first 20 and second 21 logic cells will now be described inconnection with the different logic functions used, previously mentionedin the description.

In FIG. 4 b, when the logic function is a type AND logic function, eachfirst 20 and second 21 logic cell includes an AND gate receiving theenvelope logic signal E_(j) in one of their inputs and the symbolelement a(k), b(k) respectively in the other of their inputs, in orderto deliver the validated encoded symbol S′(k) or the pause symbol Sr(k).

In FIG. 4 c, when the logic processing corresponds to a type OR logicfunction with the complemented envelope signal, the first 20 and thesecond 21 logic cells are formed by an OR gate receiving in one of theirinputs the envelope logic signal E_(j) by means of an inverter, and inthe other of their inputs, the symbol element a(k), b(k) in order todeliver the validated encoded symbol S′(k) and the pause symbol Sr(k).

In FIG. 4 d, when the logic processing corresponds to a type AND logicfunction with the complemented envelope logic signal, the first 20 andthe second 21 logic cell comprise an AND gate one of the inputs of whichreceives the envelope logic signal by means of an inverter and the otherof the inputs receives the corresponding symbol element a(k), b(k) inorder to deliver the validated encoded symbol S′(k) or the pause symbolSr(k).

In FIG. 4 e, when the logic processing corresponds to a type OR logicfunction between the symbol elements of the encoded symbols a(k), b(k)and envelope logic signal E_(j) the first 20 and the second 21 logiccell consist of a gate OR receiving, in one of their inputs the envelopelogic signal E_(j) and in the other of their inputs, the symbol elementa(k), respectively b(k) in order to deliver the validated encodedsymbols S′(k) or pause symbols Sr(k).

Finally, a non-restrictive embodiment of the discrimination module 1 ofthe encapsulation module C_(j) will be described in a preferentialversion, in connection with FIG. 5. According to the aforementioned FIG.5, the discrimination module 1 of the encapsulation message can includean alignment device 10 enabling the synchronisation word SY_(j) in theencapsulation message to be detected. The alignment device can, in astandard way, consist of a memory of sufficient size enabling a readingof the field relative to the synchronisation word SY_(j) and comparisonof the read values of this field with a reference message, marked CR. Oncorrespondence of the read values between the two fields, the memorisedvalue in the field of length L_(j) of the encapsulation message C_(j)can then be loaded into a reading circuit 11, such as shown in FIG. 5.

Finally, the discrimination module 1 of the encapsulation message caninclude also an up/down counter 12, which is loaded, from the lengthvalue read in the field L_(j), this up/down counter enabling theenvelope signal E_(j) to be generated one of the logic states of whichhas a length proportional to the aforementioned length value L_(j). Itis understood that the up/down counter plays, as it were, the role of amono-stable circuit the metastable state of which is adjusted as afunction of the length value loaded into this latter. Of course, theup/down counter is normally driven by a clock signal CK such asmentioned previously in the description.

Finally, it is desirable to point out, after the VITERBI decodingprocess applied to the aforementioned encoded signals, which are in factuseful data, i.e. the data obtained other than that in relation to thedecoding of the pause symbols.

With this object, the envelope logic signal E_(j) can therefore beshifted and delayed from the processing time necessary to the decodingof one or several data, as shown in FIG. 6, this shifted envelope logicsignal ΔE_(j) enabling in fact the data obtained by decoding of only thevalidated encoded symbols to be synchronised and discriminated.

The method for encoding, the method for decoding and the decodingdevice, the objects of the present invention, can be used in aparticularly advantageous way in all applications subjected to adigital/analogue then analogue/digital data conversion and requiring adetection of the errors correction.

They are particularly advantageous and adapted to all applications whichrequire the multiplexing of data to be carried out in the physical layerof the transmission network. Thus, all communication networks of packetsoperating transmissions in non connected mode and absolutely requiringthe use of an errors correction process can be subjected to an encodingprocess of a channel the ends of which are composed of a convolutiveencoder and a VITERBI type decoder such as described in the description.

1. A method for convolutive encoding and transmission by packets of adigital serial data series flow which is formed by a successive numberof bits of a specified value with a current bit of rank k beingdesignated as i(k), through a convolutive encoding of depth K, saidmethod comprising the steps: a) discriminating, in said series flow, aset of successive current bits, in order to form a current packet ofdigital data; b) defining for said convolutive encoding a stablestarting binary value; c) subjecting said digital data of said currentpacket to a convolutive encoding process, at each value of the currentbit i(k) corresponding to a first encoded value a(k) and a secondencoded value b(k), a set of these first and second encoded valuesconstituting an encoded symbol S(k)={a(k); b(k)}representative of thecurrent bit i(k); d) forming from the encoded symbols, a packet ofencoded symbols, by a concatenation of said encoded symbols; e)assigning to said convolutive encoding process said stable startingbinary value as a constraint value at the end of said packet of encodedsymbols; f) generating at least one encapsulation message of said packetof encoded symbols; g) transmitting, in a common message, said at leastone encapsulation message and said packet of encoded symbols fordecoding and use; and h) repeating the operations a) to g) for eachcurrent packet of digital data constituting said series flow of bits. 2.A method for decoding a digital data series flow encoded by convolutiveencoding using a stable starting binary value and transmitted bypackets, said method comprising the following steps: a) receiving apacket of encoded symbols S(k) and an encapsulation message; b)discriminating said encapsulation message in order to generate anenvelope logic signal having a first binary value prior to the start,and subsequently at the end, of said packet of encoded symbols and asecond binary value during the reception of said packet of encodedsymbols; c) subjecting said envelope logic signal and said encodedpacket of symbols to a logic processing enabling to generate; successivepause symbols of specified value and rank, on the basis of said stablestarting binary value, for said first binary value of said envelopelogic signal, and successive validated encoded symbols S′k={a′(k);b′(k)} of rank k corresponding to said packet of encodedsymbols S(k)for said secondary binary value of said envelope logicsignal; and d) subjecting said successive pause symbols and validatedencoded symbols of given rank to a continuous VITERBI type decoding,said pause symbols providing continuity of a decoding lattice byimposing a stable state between two packets of said successive validatedencoded symbols.
 3. A decoding method according to claim 2, wherein fora pause state as well as for a first logic value of said envelope logicsignal corresponding to start of a packet and end of a packet equal tothe value zero and for a second logic value of said envelope logicsignal equal to the value 1, said logic processing comprises applying toeach received symbol a(k), b(k) an AND logic function with said envelopelogic signal.
 4. A decoding method according to claim 2, wherein for apause state as well as for a first logic value of said envelope logicsignal corresponding to start of a packet and end of a packet equal tothe value 1 and for a second logic value of said envelope logic signalequal to the value 0, said logic processing comprises applying to eachreceived symbol a(k), b(k) an OR logic function with the complement ofsaid envelope logic signal.
 5. A decoding method according to claim 2,wherein for a pause state and a first logic value of said envelope logicsignal equal to the value 0 and for a signal representing activity ofthe envelope corresponding to a second logic value equal to the value 1,said logic processing comprises applying to each symbol a(k), b(k) anAND logic function with the complement of said logic signal.
 6. Adecoding method according to claim 2, wherein for a pause state and afirst logic value of said envelope logic signal equal to the value 1,and for a signal representing the activity of the envelope correspondingto a second logic value equal to 0, said logic processing comprisesapplying to each symbol a(k), b(k) an OR function with said envelopelogic signal.
 7. A decoding device for a series flow of digital dataencoded by convolutive encoding using a stable starting binary value andtransmitted by packets comprising: means for receiving a packet ofencoded symbols S(k) and an encapsulation message; means fordiscriminating said encapsulation message so as to enable an envelopelogic signal to be generated for said packet, said envelope logic signalhaving a first binary value before the beginning and after the end ofthe packet of encoded symbols and a second binary value during thereception of the packet of encoded symbols; logic processing means forgenerating: successive pause symbols of specified value and rank, on thebasis of said stable starting binary value of the received packet, forsaid first binary value of said envelope logic signal, and successivevalidated encoded symbols S′ k={a′(k); b′(k)} of rank k corresponding tosaid packet of encoded symbols S(k) for said second binary value of saidenvelope logic signal; and VITERBI decoding means for carrying out, onthe basis of said successive pause symbols and said validated encodedsymbols of given rank, a continuous VITERBI type decoding, said pausesymbols providing continuity of a decoding lattice by imposing a stablestate between two packets of said successive validated encoded symbols.8. A device according to claim 7, wherein said logic processing meansinclude at least: a first logic cell receiving, in a first input, eachfirst symbol element a(k), and, in a second input, said envelope logicsignal and delivering a first validated symbol element a′(k); a secondlogic cell receiving, in a first input, each second symbol element b(k),and, in a second input, said envelope logic signal and delivering asecond validated symbol element b′(k).
 9. A device according to claim 8,wherein said first and second logic cells are constituted by anidentical logic gate, each provided with a first input and a secondinput, the first input of each logic gate constituting the first inputof each logic cell and the second in put of each logic gate beingconnected to the second input of each logic cell directly or by means ofa logic inverter, as a function of the logic value assigned to the firstand second binary value of said envelope logic signal respectively. 10.A method for convolutive encoding and transmission by packets of adigital data series flow which is formed by successive number of bits ofa specified value with a current bit of rank k being designated as i(k),through a convolutive encoding of depth K, said method comprising thefollowing steps: a) discriminating, in said series flow, a set ofsuccessive current bits, in order to form a current packet of digitaldata; b) defining for said convolutive encoding a stable starting binaryvalue; c) subjecting said digital data of said current packet to aconvolutive encoding process, at each value of the current bit i(k)corresponding to a first encoded value a(k) and a second encoded valueb(k), a set of the first and second encoded values constituting anencoded symbol S(k)=a{(k); b(k)}representative of the current bit i(k)and a plurality of encoded symbols being generated; d) forming, from theencoded symbols, a packet of encoded symbols, by a concatenation of saidencoded symbols; e) assigning to said convolutive encoding process saidstable starting binary value as a constraint value at the end of saidpacket of encoded symbols; f) generating at least one encapsulationmessage of said packet of encoded symbols, said message comprising apacket length field; g) transmitting, in a common message, said at leastone encapsulation message and said packet of encoded symbols fordecoding and use; and h) repeating the operations a) to g) for eachcurrent packet of digital data constituting said series flow of bits.11. A method for decoding a digital data series flow encoded byconvolutive decoding using a stable starting binary value andtransmitted by packets, comprising the following steps: a) receiving apacket of encoded symbols S(k) and an encapsulation message comprising afield Indicating the length of said packet of encoded symbols; b)discriminating said encapsulation message in order to generate, on thebasis of the packet length, an envelope logic signal having a firstbinary value prior to the start and subsequently at the end of saidpacket of encoded symbols and a second binary value during the receptionof said packet of encoded symbols; c) subjecting said envelope logicsignal and said packet of encoded symbols to a logic processing enablingto generate: successive pause symbols of specified value and rank, onthe basis of said stable starting binary value, for said first binaryvalue of said envelope logic signal, and successive validated encodedsymbols S′k={a′(k); b′(k)} of rank k corresponding to said packets ofencoded symbols S(k) for said second binary value of said envelope logicsignal; and d) subjecting said successive pause symbols and validatedencoded symbols of given rank to a continuous VITERBI type decoding,said pause symbols providing continuity of a decoding lattice byimposing a stable state between two packets of said successive validatedencoded symbols.
 12. A decoding method according to claim 11, whereinfor a pause state as well as for a first logic value of said envelopelogic signal corresponding to start of a packet and end of a packetequal to the value of zero and for a second logic value of said envelopelogic signal equal to the value 1, said logic processing comprisesapplying to each received symbol a(k), b(k) an AND logic function withsaid envelope logic signal.
 13. A decoding method according to claim 11,wherein for a pause state as well as for a first logic value of saidenvelope logic signal corresponding to start of a packet and end of apacket equal to the value 1 and for a second logic value of saidenvelope logic signal equal to the value 0, said logic processingcomprises applying to each received symbol a(k), b(k) an OR logicfunction with the complement of said envelope logic signal.
 14. Adecoding method according to claim 11, wherein for a pause state and afirst logic value of said envelope logic signal equal to the value of 0,and for a signal representing activity of the envelope corresponding toa second logic value equal to the value 1, said logic processingcomprises applying to each symbol a(k), b(k) an AND logic function withthe complement of said envelope logic signal.
 15. A decoding methodaccording to claim 11, wherein for a pause state and a first logic valueof said envelope logic signal equal to the value 1, and for a signalrepresenting activity of the envelope corresponding to a second logicvalue equal to 0, said logic processing comprises applying to eachsymbol a(k), b(k) an OR logic function with said envelope logic signal.16. A decoding device for a series flow of digital data encoded byconvolutive encoding using a stable starting binary value andtransmitted by packets, said device comprising: means for receiving apacket of encoded symbols S(k) and an encapsulation message comprising afield indicating the length of the packet of encoded symbols; means fordiscriminating said encapsulation message for enabling an envelope logicsignal to be generated for said packet, on the basis of the packetlength, said envelope logic signal having a first binary value prior tothe start and subsequently at the end of the packet of encoded symbolsand a second binary value during receiving of the packet; logicprocessing means for generating: successive pause symbols of specifiedvalue and rank, on the basis of said stable starting binary value, forsaid first binary value of said envelope logic signal, and successivevalidated encoded symbols S′k={a′(k); b′(k)} of rank k corresponding tosaid packet of encoded symbols S(k) for said second binary value of saidenvelope logic signal; and VITERBI decoding means for carrying out, onthe basis of said successive pause symbols and validated encoded symbolsof given rank, a continuous VITERBI type decoding, said pause symbolsproviding continuity of a decoding lattice by imposing a stable statebetween two packets of said successive validated encoded symbols.
 17. Adevice according to claim 16, wherein said logic processing meansinclude at least: a first logic cell receiving, in a first input, eachfirst symbol element a(k), and, in a second input, said envelope logicsignal, and delivering a first validated symbol element a′(k); and asecond logic cell receiving, in a first input, each second symbolelement b(k), and, in a second input, said envelope logic signal, anddelivering a second validated symbol element b′(k).
 18. A deviceaccording to claim 17, wherein each of said first logic cell and saidsecond logic cell comprises an identical logic gate, each gate having afirst input and a second input, the first input of each logic gateconstituting the first input of each logic cell and the second input ofeach logic gate being connected to the second input of each logic celldirectly or by means of a logic inventer, as a function of the logicvalue assigned to the first and second binary value of said envelopelogic signal, respectively.